Nazanin Magharei, Reza Rejaie

1
PRIME P2P Receiver-drIven MEsh based Streaming

• Nazanin Magharei, Reza Rejaie
• University of Oregon
• http//mirage.cs.uoregon.edu

2
Introduction

• One-to-many streaming of live multimedia
  content over the Internet is very popular, e.g.
  IPTV
• P2P overlays offer a promising approach for
  scalable streaming of live content over the
  Internet
• Goal Maximizing delivered quality to individual
  peers in a scalable fashion
• Challenges Bandwidth heterogeneity asymmetry,
  churn
• A common approach is to push sub-streams of
  content through multiple trees gt limited
  scalability
• Pull content delivery is a promising alternative
• Can we design a pull-based content delivery for
  live P2P streaming that scales with the no of
  peers?

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Mesh-based P2P Streaming

• Overlay Construction Peers form a randomly
  connected mesh
• Content Delivery periodic reporting pull
  requesting (swarming)
• Key component a packet scheduling mechanism at
  each peer determines which packets should be
  pulled from each parent
• File swarming mechanisms (e.g. BitTorrent)
  leverages the availability of the entire file
  the elastic nature of the content
• Distribute pieces of a file among different
  peers
• Peers exchange (swarm) their available pieces
  with each other
• Peers outgoing bandwidth can be effectively
  utilized ? scalable
• How can swarming be incorporated into live P2P
  streaming?

4
Mesh-based P2P Streaming

• Incorporating a swarming content delivery into
  live P2P streaming is challenging because
• Swarming does not accommodate in-time
  requirement of streaming content delivery
• Live streaming provides limited amount of
  content for effective swarming
• Status of existing mesh-based approaches
• A couple of mesh-based P2P streaming mechanisms
  have been presented, e.g. CoolStreaming, ChainSaw
• Various extensions of BitTorrent that
  incorporate timing
• Few systems that claim to do this

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This paper

• examines how swarming content delivery can be
  incorporated into live P2P streaming
• explores fundamental design tradeoffs
• between overlay connectivity, peer population,
  packet scheduling, buffer requirement at each
  peer, ...
• presents a methodology to identify performance
  bottlenecks
• Using a new mesh-based P2P mechanism, called
  PRIME
• Our focus is on live streaming

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Swarming Content delivery

• Parents progressively report their available
  content
• Packet scheduling mechanism at each peer
  periodically (once per D sec) determines packets
  to be pulled from each parent
• All connections are congestion controlled (RAP
  or TFRC)
• To accommodate bandwidth heterogeneity, content
  is MDC encoded
• Live source generates a new segment of length D
  once every D sec
• segment packets of all descriptions with
  timestamps within t1,t1D
• Peers delay their playout time by wD sec behind
  source to accommodate swarming
• each peer buffer at least wD sec worth of
  content
• What is the proper packet scheduling mechanism
• to maximize delivered quality and minimize buffer
• requirement at individual peers?

tp130sec
Source
tp100sec
tp100sec
5
2
1
4
tp100sec
tp100sec
3
6
tp100sec
tp100sec
wD 30 sec
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Performance bottlenecks

• Goal each peer expects to receive maximum
  deliverable quality through its access link
• Two possible performance bottlenecks that may
  limit the delivered quality to each peer
• Bandwidth bottleneck Insufficient aggregate
  bandwidth from all parents
• Content bottleneck Insufficient useful content
  from all parents
• How to decouple bandwidth and content
  bottleneck?
• At each packet transmission time, if there is no
  outstanding requested packet to send, parents
  send a marked packet with the same size as data
  packet
• How can we minimize these bottlenecks?

p2
p3
p1
Incoming Access-link
c
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Addressing bandwidth bottleneck
Performance bottleneck

• Prior studies often assumed a fix peer degree
• Bandwidth bottleneck only depends on overlay
  topology
• Incoming/outgoing bandwidth degree of
  participating peers
• Avg. BW for a connection between parent p and
  child c
• MIN (outbwp/outdegp, inbwc/indegc)
• BW-Degree Condition
• for any peer i, j outbwi/outdegi inbwj/indegj
  bwpf
• All connections in the overlay have roughly the
  same average bandwidth
• This leads to a high BW utilization for all
  participating peers especially in heterogeneous
  scenarios (see simulation results in the paper)
• What is a good ratio of bandwidth to degree?

outdegp
p
indegc
c
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Addressing content bottleneck
Performance bottleneck

• Content bottleneck depends on both overlay
  topology content delivery
• data unit bwpf D
• Each parent peer should have at least one useful
  data unit per interval D for each one of its
  child peer to avoid content bottleneck
• The availability of new data units at each
  parent peer is determined by global pattern of
  content delivery
• Global pattern depends on the collective
  behavior of packet scheduling mechanisms at
  individual peers
• What global pattern of delivery minimizes
  content bottleneck among peers?
• What packet scheduling leads to the desired
  global pattern?

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Global pattern of content delivery
Addressing content bottleneck

• Organized View Group peers into levels based on
  their shortest distance from source
• See the paper for more details on this
• Intuitively, the pattern of delivery for a
  segment that minimizes content bottleneck has 2
  phases
• Diffusion phase All participating peers should
  receive a data unit of the segment as fast as
  possible
• Swarming phase Peers can exchange (swarm)
  their data units with each other until they
  receive their desired quality of the segment

SRC
Level 1
1
3
2
Level 2
6
4
7
5
Level 3
10
12
13
8
9
11
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Diffusion phase of a segment
Global pattern of content delivery

• Fastest time for pulling all data units of a
  segment from source to the lowest level
  depthD sec
• All peers in a subtree rooted
• at a peer in level 1 receive the same
• data unit in a diffusion phase - diffusion
  subtree
• The number of diffusion subtrees is equal
  to the source degree

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Swarming phase of a segment
Global pattern of content delivery
t02D,t03D
t03D,t04D

• Only swarming parents on different diffusion
  subtrees can rapidly provide a new data unit
• Swarming phase at individual peers may take one
  or more intervals depending on the location of
  their swarming parents
• How many intervals is sufficient for swarming?
• Kmin minimum of swarming intervals
  for which 90 of peers quality gt 90
• Total number of intervals for delivery
  of a segment (wmin ) diffusion intervals
  (depth) swarming intervals (Kmin )

2
1
3
6
7
4
5
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Packet scheduling
Addressing content bottleneck

• The collective behavior of packet scheduling in
  individual peers leads to the desired global
  pattern of content delivery
• Should identify timestamp, then parent and
  description for each packet
• New packets ? from diffusion parent(s)
• Playing packets ? from swarming parents
• Swarming packets ? from swarming parents
• See the paper for further details

Swarming win.
Playing win.
New win.
Target quality
tp
Sources playout time
tmax-last
tmax
D
w
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Performance Evaluation

• Using ns2 simulator to properly examine the
  effect of packet level dynamics and packet loss
• Use BRITE topology generator with 10 AS and 10
  routers in each AS
• RED queue management on all routers
• Bandwidth bottlenecks are at the edge
• Use RAP as a congestion control mechanism
• Encoded streams with MDC with 160 kbps BW/decs
• BW-Degree condition is enforced in all
  simulations
• D is set to 6 sec
• Two scenarios 200 peers with homogeneous and
  symmetric bandwidth
• scenario 700 peers access link BW 700 kbps,
  max. quality 5 descriptions
• scenario 1.5 peers access link BW 1.5 Mbps,
  max. quality 10 descriptions
• Focus on the behavior of the system in steady
  state

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What is a proper peer degree?
Evaluation overlay properties
of population with quality gt 90
Degree

• w depth 3 , Kmin is fixed across different
  degrees
• A sweet range of peer degrees to achieve good
  performance
• Low degree limited diversity of available
  content leads to content bottleneck ? does not
  depend on peers BW
• High degree high loss rate leads to content
  bottleneck ? depends on bwpf thus peer BW

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Duration of each phase
Overlay Properties
Kmin
Depth
Degree

• depth slowly decreases independent of peers
  bandwidth
• By increasing degree from 4 to 6, Kmin reaches
  to its minimum value of 3
• Further increase in peer degree increases Kmin

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Pattern of content delivery
Overlay Properties
700 kbps scenario
CDF
Avg. hop count

• Average path length decreases with peer degree
  due to the decrease in depth
• Distribution of path length becomes more
  homogeneous due to the increase in diversity
  among parents
• Lost packets are requested from the same
  swarming parent

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Bandwidth heterogeneity
Overlay Properties

• How are the delivered quality and buffer
  requirements for high bandwidth peers affected by
  the presence of low BW peers?
• None of the following factors has a significant
  effect on performance
• Degree of BW heterogeneity
• Fraction of high bandwidth peers
• Location of high bandwidth peers

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Peer population
Evaluation
BW 700 kbps Degree 6
Interval
Peer population

• How does the buffer requirement at each peer (w)
  change with peer population?
• depth gradually increases by peer population
• Swarming intervals (Kmin) does not change with
  peer population since the number of diffusion
  subtrees is fixed
• wmin gradually increases with population ?
  scalability

20
Conclusions

• Presented PRIME, a new protocol for live P2P
  mesh-based streaming of live content
• Illustrated several key design tradeoff s in
  incorporating swarming
• sketched a methodology to identify performance
  bottlenecks
• Ongoing Work
• Incorporating contribution awareness into
  mesh-based streaming
• Systematic evaluations of packet scheduling
  mechanisms
• Dynamic addition of resources to offer QoS
• Distributed, uncoordinated P2P video caching
• for more information visit http//mirage.cs.uoreg
  on.edu